1. Field of the Industrial Application
The invention described herein relates to a laminator for bonding a film onto a panel, and more particularly to a pressurizing roller used to bond a film onto a panel.
2. Description of the Prior Art
A process of manufacturing a printed circuit board used for electronic equipment, such as a computer, includes a step of bonding a laminated material onto a panel for the printed circuit board. The laminated material is made up of a photo-sensitive resin layer (resist layer) and a transparent resin film. The photo-sensitive resin layer is bonded directly onto the surface of the panel, and the transparent resin film is formed on the photo-sensitive resin layer.
The laminated material is bonded onto the panel with a laminator which has been disclosed, for instance, by Japanese Patent Application (OPI) No. 117487/1988 (the term "OPI" as used herein means an "unexamined published application") filed by the present applicant. That is, the laminated material is bonded onto the panel with the laminator as follows:
First, a panel conveying mechanism is operated to convey the panel until the front end portion, in the direction of conveyance, of the panel reaches a film bonding position. The laminated material in the form of a belt is supplied from a film supply roller. The transparent resin film on the front end portion, in the direction of conveyance, of the belt-shaped laminated material is vacuum held with a main vacuum plate (film supplying member). The main vacuum plate has a temporary film bonding member at its end which is on the side of the film bonding position. The temporary film bonding member draws the front end portion of the laminated material thereto. The temporary film bonding member has vacuum holes communicated with a vacuum system to draw the laminated material thereto, and incorporates a heater for temporarily bonding the front end portion of the laminated material.
The main vacuum plate and the temporary film bonding member are allowed to approach the film bonding position (the surface of the front end portion of the panel). Under this condition, the front end portion of the laminated material abuts against the surface of the front end portion of the panel, and the former is temporarily bonded to the latter as the temporary film bonding member generates heat.
Thereafter, the drawing operations of the main vacuum plate and the temporary film bonding member are suspended, and the main vacuum plate and the temporary film bonding member are moved away from the film bonding position. In this operation, the front end portion of the laminated material is held at the film bonding position, because it has been temporarily bonded onto the surface of the panel.
Under this condition, a hot pressurizing roller which is being rotated is caused to approach the film bonding position to push the bonded portion of the laminated material. As the hot pressurizing roller is being rotated, the laminated material is continuously bonded to the surface of the panel, while the panel is conveyed. Since, as was described above, the hot pressurizing roller is rotated while the panel is conveyed, the laminated material is automatically supplied to the film bonding position.
While the laminated material is being bonded to the surface of the panel, the rear end of the panel is detected to provide a detection signal. In response to the detection signal, the laminated material being supplied is cut to a length corresponding to the length of the panel measured in the direction of conveyance. The laminated material is cut with a cutter as follows: A sub-vacuum plate provided on the path of the laminated material is operated to draw and retain the laminated material at its cutting position (downstream of the laminated material), and under this condition the cutter is moved across the elongated laminated material to cut the latter. The cutter is a disk- shaped cutter. The rear end portion of the laminated material thus cut is drawn and retained with a vacuum bar (film rear end vacuuming and retaining member), and is then guided, under predetermined tension, to the rear end portion of the panel. The rear end portion of the laminated material is thermally bonded to the surface of the rear end portion of the panel with the hot pressurizing roller.
The panel, to which the laminated material has been bonded as described above, is conveyed to the following station where an exposure unit is provided.
A film bonding technique of this type, in which a part of the laminated material is temporarily bonded to the panel, and then the laminated material is thermally bonded to the panel, has been disclosed, for instance, by West Germany Patent DE 3334009 C2 and Japanese Patent Application Publication No. 49169/1987.
The pressurizing roller used to bond the film on the panel is as shown in FIG. 5. The outer cylindrical wall of a cylinder 101 of aluminum is covered with a rubber layer 102 about 4 mm in thickness. The cylinder 101 has a central through-hole into which a sheathed heater 103 is inserted to heat the pressurizing roller 100.
Pipe-shaped iron roller shafts 104A and 104B are fitted into holes, respectively, which are formed in both end faces of the pressurizing roller 100 in such a manner that they are in alignment with the central through-hole mentioned above. The roller shafts serve as the rotary shafts of the pressurizing roller 100. A slip ring is mounted on the shaft 104 so as to supply current to the sheathed heater 103 through electrical wires 105. The sheathed heater 103 is provided with a temperature detector which is brought into contact with the surface of the pressurizing roller, and a temperature controller which, in response to the output signal of the temperature detector, controls the voltage applied to the sheathed heater 103. Thus, with the aid of these elements, the temperature of the surface of the pressurizing roller is maintained at about 100.degree..
Films are bonded to a panel 106 as shown in FIG. 6 (an explanatory diagram of a film path as viewed from the side of a laminator). Upper and lower film rollers 107A and 107B supply films, each of which is of a three-layer structure. The non-peeled surface of each film with one layer peeled is brought into contact with the respective pressurizing roller through a winding angle of about 60.degree.. Accordingly, the peeled surfaces of the films, while being confronted with each other, are conveyed in the direction of movement of the panel 106 between upper and lower pressurizing rollers 100A and 100B in such a manner that the panel 106 is located between the peeled surfaces of the films. Under this condition, the upper and lower pressurizing rollers 100A and 100B are pushed in a direction against each other. Thus, as the panel 106 passes through the upper and lower pressurizing rollers 100A and 100B, the films are bonded to the panel.
The surfaces of the upper and lower pressurizing rollers 100A and 100B are spaced about 10 mm from each other. The lower pressurizing roller 100B is not movable, because bearings mounted on its roller shafts 104A and 104B are secured to a stationary member with screws. And a driving gear is secured to the roller shaft 104A with screws.
On the other hand, bearings mounted on the roller shafts 104A and 104B of the upper pressurizing roller 100A are secured to a vertically movable member. Thus, as the vertically movable member is moved vertically by an elastic force or air pressure, the upper pressurizing roller 100A is moved into or out of engagement with the lower pressurizing roller 100B.
Similarly as in the case of the lower pressurizing roller 100B, a driving gear is secured to the roller shaft 104A of the upper pressurizing roller 100A with screws.
The upper and lower pressurizing rollers 100A and 100B abut one another by the force applied to the roller shafts 104A and 104B through the bearings of the upper pressurizing roller.
The bearings mounted on the roller shafts 104A and 104B are spaced about 700 mm from each other. A force of about 100 kgf applied to the roller shafts 104A and 104B is applied to the bearings.
FIG. 7 is a side view showing a laminator provided with pressurizing rollers of a non-heating type, each of which is made of a rigid cylindrical pipe of stainless steel having a surface coated with "Teflon". The pressurizing rollers are so designed that the rigid cylindrical pipes themselves are rotary shafts, and are scarcely bent by any bending moment. Accordingly, the pressurizing rollers 109A and 109B are abutted against each other uniformly over their entire width. However, since the pressurizing rollers are of non-heating type as was described above, it is difficult to sufficiently bond the films to the panel. In order to eliminate this difficulty, film preheating units 110A and 110B of metal, which are each arcuate and called "heat shoes", are provided upstream of the pressurizing rollers 109A and 109B, respectively.
The film preheating units (heat shoes) 110A and 110B are stationary, and incorporate sheathed heaters.
The surface of each film preheating unit, with which the non-peeled surface of the corresponding film is brought into slide contact through a film winding angle of 180.degree. is coated with "Teflon", and its temperature is controlled to about 110.degree. C. by the sheathed heater buried in the film preheating unit.
The films are bonded to the panel 106 in the same manner as in the laminator shown in FIG. 6.
That is, the upper and lower film preheating units (heat shoes) 110A and 110B, on which the non-peeled surfaces of the films are wound, are secured to two side boards with screws in such a manner that they are spaced about 10 mm from each other. The panel is moved into the space between the upper and lower preheating units (heat shoes) 110A and 110B. Thus, while the panel is being moved through the upper and lower pressurizing rollers confronted with each other, the peeled surfaces of the films are bonded to the panel.
Problems to be Solved by the Present Invention
In FIG. 5, the distance between the bearings mounted on the roller shafts 104A and 104B is about 700 mm, and the force of about 100 kgf applied to the roller shafts 104A and 104B is applied to the pressurizing rollers 100A and 100B, as was described above. When the upper and lower pressurizing rollers 100A and 100B are pushed against each other, a bending moment acts on the roller shafts 104A and 104B, so that the middle portion of each of the pressurizing rollers 100A and 100B exerts less pressure than the other portions.
That is, it is difficult for each of the pressurizing rollers 100A and 100B to provide uniform pressure over the entire length thereof.
The pressure width may be increased by increasing the force applied to the movable member. However, as the force is increased, in each of the pressurizing rollers 100A and 100B, the difference between the pressure at the middle portion and the pressure at the right or left end portion is increased. That is, merely increasing the force applied to the movable member is not suitable for making the distribution of pressure uniform.
If the film bonding operation is carried out under the condition that the pressurizing rollers are not uniform in the distribution of pressure, then the films are not uniformly bonded to the panel; that is, the films are not sufficiently bonded to the part of the panel where the pressure is lower. In addition, the non-uniform distribution of pressure; i.e., the difference in pressure may cause the panel to meander, and the meandering of the panel may form wrinkles on the films.
Even if the pressurizing rollers are uniform in the distribution of pressure, it is necessary to use an elastic member of rubber or the like to push the films against the panel. Otherwise the unevenness of the panel may make it difficult to uniformly bond the films to the panel.